It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves under certain engine load conditions.
For an overhead-cam engine, a known approach is to equip the hydraulic lash adjusters for those valvetrains with means whereby the roller finger followers (RFFs) may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated valves. Such lash adjusters are known in the art as Deactivating Hydraulic Lash Adjusters (DHLAs).
A prior art DHLA includes a conventional hydraulic lash elimination means disposed in a plunger having a domed head for engaging the RFF. The plunger itself is slidably disposed in a pin housing containing the lock pins which in turn is slidably disposed in a DHLA body. The pin housing may be selectively latched and unlatched hydromechanically to the body by the selective engagement of a spring and pressurized engine oil on lock pins.
During engine operation in valve deactivation mode, the lock pins are withdrawn from lock ledges in the body, which may be an annular groove, and the pin housing is reciprocally driven in oscillation by the socket end of the RFF which pivots on its opposite pad end on the immobile valve stem as the cam lobe actuates the RFF. The pin housing is returned during half the lost motion reciprocal cycle by one or more lost motion springs disposed within the body.
In a prior art DHLA, the angular orientation of the DHLA body is not specified with respect to the cylinder head. As a result, the axis of the lock pins is free to assume any random orientation, even for the case when the orientation of the pin housing is fixed relative to the body. This variability in orientation can result in the problem of unequal load sharing for locking mechanisms utilizing two pins, the solution to which is the subject of the present invention.
During valve actuation, the displacement of the RFF by the cam lobe creates cyclically-imposed force vectors on the head of the DHLA plunger. Specifically, as the RFF roller climbs the opening flank of the cam eccentric, the RFF body is urged in a first direction transverse to the axis of the camshaft; and as the RFF roller descends the closing flank of the cam eccentric, the RFF body is urged in a second and opposite direction. Since the orientation of the lock pin axis is not explicitly specified, there are times when the pin axis will assume an orientation co-planar with the cyclic side loads described above. In this situation (wherein the pin axis is perpendicular to the axis of the camshaft), when the side loads reach a sufficient magnitude relative to the axial load, the entire load is entirely supported by only one of the lock pins. When the side load subsequently changes direction, the aforesaid pin is completely unloaded and the other pin assumes the full axial load. Instead of both pins equally sharing the axial load as desired, the lock pins cyclically alternate between supporting the entire load individually and being totally unloaded.
This problem can be relieved by orienting the lock pin axis to be substantially parallel to the axis of the camshaft, thus enabling both lock pins to share the torque load equally. Such orientation can also be used to locate vulnerable points, known in the art as “stress risers”, in the DHLA body and pin housing in positions of low tensile stress.
What is needed in the art is an improved arrangement for fixing the orientation of a DHLA body within a bore in an engine head such that the axis of the lock pins in the pin housing is always parallel to the axis of the engine camshaft.
It is a principal object of the present invention to reduce wear in, and extend the operating life of, a deactivating hydraulic lash adjuster in an internal combustion engine.